Identification of Cadherin 2 ( CDH2 ) Mutations in Arrhythmogenic Right Ventricular Cardiomyopathy

Unveiling the Spectrum of Minor Genes in Cardiomyopathies: A Narrative Review

Hereditary cardiomyopathies (CMPs), including arrhythmogenic cardiomyopathy (ACM), dilated cardiomyopathy (DCM), and hypertrophic cardiomyopathy (HCM), represent a group of heart disorders that significantly contribute to cardiovascular morbidity and mortality and are often driven by genetic factors. Recent advances in next-generation sequencing (NGS) technology have enabled the identification of rare variants in both well-established and minor genes associated with CMPs. Nowadays, a set of core genes is included in diagnostic panels for ACM, DCM, and HCM. On the other hand, despite their lesser-known status, variants in the minor genes may contribute to disease mechanisms and influence prognosis. This review evaluates the current evidence supporting the involvement of the minor genes in CMPs, considering their potential pathogenicity and clinical significance. A comprehensive analysis of databases, such as ClinGen, ClinVar, and GeneReviews, along with recent literature and diagnostic guidelines provides a thorough overview of the genetic landscape of minor genes in CMPs and offers guidance in clinical practice, evaluating each case individually based on the clinical referral, and insights for future research. Given the increasing knowledge on these less understood genetic factors, future studies are essential to clearly assess their roles, ultimately leading to improved diagnostic precision and therapeutic strategies in hereditary CMPs.

Genome-wide association study of therapeutic response to statin drugs in cardiovascular disease

Cardiovascular disease (CVD) is one of the main causes of death in the world. The increased level of blood cholesterol is significantly correlated to CVD incidents. Statins are a group of drugs that decrease the synthesis of cholesterol in the liver by inhibiting the final enzyme of the pathway named HMG-CoA reductase. Several investigations showed that different patients give different responses to the administration of statin drugs according to their genetic background. In this research study, using Genome-Wide Association Studies (GWAS) data analysis methods, such as the SimpleM statistical approach and genomic connection matrix, we tried to discover the novel candidate SNPs that were involved in response to statin drugs. The investigation was carried out using 3,221 cardiovascular patients' data about genotypes and phenotypes of two important parameters including total cholesterol, and LDL level, in response to statin administration. Functional annotation of nearest genes to candidate SNPs was also carried out by using comprehensive databases and tools such as BioMart-Ensembl, UCSC, NCBI, and WebGestalt software. Our results represented eight novel SNPs (rs10820084, rs4803750, rs10989887, rs1966503, rs17502794, rs10785232, rs484071, rs4785621) significantly associated with statin response in different individual cardiovascular patients for the first time. In addition, the groups of genes that are close to the SNPs were also represented and evaluated in detail. Our results illustrated that some of the genes such as BAAT, BCL3, and CMTM6 have a direct functional impact on cholesterol level or LDL biosynthesis which confirmed the effects of neighbor SNPs on the response to statin drugs. Today, finding the loci, genes, and molecular mechanisms involved in the response to drugs is of great importance in pharmacogenomics and personalized medicine.

In Vivo Approaches to Understand Arrhythmogenic Cardiomyopathy: Perspectives on Animal Models

Arrhythmogenic cardiomyopathy (AC) is a hereditary cardiac disorder characterized by the gradual replacement of cardiomyocytes with fibrous and adipose tissue, leading to ventricular wall thinning, chamber dilation, arrhythmias, and sudden cardiac death. Despite advances in treatment, disease management remains challenging. Animal models, particularly mice and zebrafish, have become invaluable tools for understanding AC's pathophysiology and testing potential therapies. Mice models, although useful for scientific research, cannot fully replicate the complexity of the human AC. However, they have provided valuable insights into gene involvement, signalling pathways, and disease progression. Zebrafish offer a promising alternative to mammalian models, despite the phylogenetic distance, due to their economic and genetic advantages. By combining animal models with in vitro studies, researchers can comprehensively understand AC, paving the way for more effective treatments and interventions for patients and improving their quality of life and prognosis.

A Comprehensive Analysis of Non-Desmosomal Rare Genetic Variants in Arrhythmogenic Cardiomyopathy: Integrating in Padua Cohort Literature-Derived Data

Arrhythmogenic cardiomyopathy (ACM) is an inherited myocardial disease at risk of sudden death. Genetic testing impacts greatly in ACM diagnosis, but gene-disease associations have yet to be determined for the increasing number of genes included in clinical panels. Genetic variants evaluation was undertaken for the most relevant non-desmosomal disease genes. We retrospectively studied 320 unrelated Italian ACM patients, including 243 cases with predominant right-ventricular (ARVC) and 77 cases with predominant left-ventricular (ALVC) involvement, who did not carry pathogenic/likely pathogenic (P/LP) variants in desmosome-coding genes. The aim was to assess rare genetic variants in transmembrane protein 43 (TMEM43), desmin (DES), phospholamban (PLN), filamin c (FLNC), cadherin 2 (CDH2), and tight junction protein 1 (TJP1), based on current adjudication guidelines and reappraisal on reported literature data. Thirty-five rare genetic variants, including 23 (64%) P/LP, were identified in 39 patients (16/243 ARVC; 23/77 ALVC): 22 FLNC, 9 DES, 2 TMEM43, and 2 CDH2. No P/LP variants were found in PLN and TJP1 genes. Gene-based burden analysis, including P/LP variants reported in literature, showed significant enrichment for TMEM43 (3.79-fold), DES (10.31-fold), PLN (117.8-fold) and FLNC (107-fold). A non-desmosomal rare genetic variant is found in a minority of ARVC patients but in about one third of ALVC patients; as such, clinical decision-making should be driven by genes with robust evidence. More than two thirds of non-desmosomal P/LP variants occur in FLNC.

Personalized transcriptome signatures in a cardiomyopathy stem cell biobank

BACKGROUND

There is growing evidence that pathogenic mutations do not fully explain hypertrophic (HCM) or dilated (DCM) cardiomyopathy phenotypes. We hypothesized that if a patient's genetic background was influencing cardiomyopathy this should be detectable as signatures in gene expression. We built a cardiomyopathy biobank resource for interrogating personalized genotype phenotype relationships in human cell lines.

METHODS

We recruited 308 diseased and control patients for our cardiomyopathy stem cell biobank. We successfully reprogrammed PBMCs (peripheral blood mononuclear cells) into induced pluripotent stem cells (iPSCs) for 300 donors. These iPSCs underwent whole genome sequencing and were differentiated into cardiomyocytes for RNA-seq. In addition to annotating pathogenic variants, mutation burden in a panel of cardiomyopathy genes was assessed for correlation with echocardiogram measurements. Line-specific co-expression networks were inferred to evaluate transcriptomic subtypes. Drug treatment targeted the sarcomere, either by activation with omecamtiv mecarbil or inhibition with mavacamten, to alter contractility.

RESULTS

We generated an iPSC biobank from 300 donors, which included 101 individuals with HCM and 88 with DCM. Whole genome sequencing of 299 iPSC lines identified 78 unique pathogenic or likely pathogenic mutations in the diseased lines. Notably, only DCM lines lacking a known pathogenic or likely pathogenic mutation replicated a finding in the literature for greater nonsynonymous SNV mutation burden in 102 cardiomyopathy genes to correlate with lower left ventricular ejection fraction in DCM. We analyzed RNA-sequencing data from iPSC-derived cardiomyocytes for 102 donors. Inferred personalized co-expression networks revealed two transcriptional subtypes of HCM. The first subtype exhibited concerted activation of the co-expression network, with the degree of activation reflective of the disease severity of the donor. In contrast, the second HCM subtype and the entire DCM cohort exhibited partial activation of the respective disease network, with the strength of specific gene by gene relationships dependent on the iPSC-derived cardiomyocyte line. ADCY5 was the largest hubnode in both the HCM and DCM networks and partially corrected in response to drug treatment.

CONCLUSIONS

We have a established a stem cell biobank for studying cardiomyopathy. Our analysis supports the hypothesis the genetic background influences pathologic gene expression programs and support a role for ADCY5 in cardiomyopathy.

Understanding Arrhythmogenic Cardiomyopathy: Advances through the Use of Human Pluripotent Stem Cell Models

Cardiomyopathies (CMPs) represent a significant healthcare burden and are a major cause of heart failure leading to premature death. Several CMPs are now recognized to have a strong genetic basis, including arrhythmogenic cardiomyopathy (ACM), which predisposes patients to arrhythmic episodes. Variants in one of the five genes (PKP2, JUP, DSC2, DSG2, and DSP) encoding proteins of the desmosome are known to cause a subset of ACM, which we classify as desmosome-related ACM (dACM). Phenotypically, this disease may lead to sudden cardiac death in young athletes and, during late stages, is often accompanied by myocardial fibrofatty infiltrates. While the pathogenicity of the desmosome genes has been well established through animal studies and limited supplies of primary human cells, these systems have drawbacks that limit their utility and relevance to understanding human disease. Human induced pluripotent stem cells (hiPSCs) have emerged as a powerful tool for modeling ACM in vitro that can overcome these challenges, as they represent a reproducible and scalable source of cardiomyocytes (CMs) that recapitulate patient phenotypes. In this review, we provide an overview of dACM, summarize findings in other model systems linking desmosome proteins with this disease, and provide an up-to-date summary of the work that has been conducted in hiPSC-cardiomyocyte (hiPSC-CM) models of dACM. In the context of the hiPSC-CM model system, we highlight novel findings that have contributed to our understanding of disease and enumerate the limitations, prospects, and directions for research to consider towards future progress.

Evolving spectrum of arrhythmogenic cardiomyopathy: Implications for Sports Cardiology

Arrhythmogenic cardiomyopathy (ACM) is a genetic heart muscle disease, structurally characterized by progressive fibro-fatty replacement of the normal myocardium and clinically by ventricular arrhythmias (VAs). Predominantly thanks to the use of cardiac magnetic resonance, we have learnt that the spectrum of the disease encompasses not only the classical right ventricular phenotype, but also biventricular and left dominant variants. Sport activity contributes to the phenotypic expression and progression of ACM and may trigger life-threatening VAs and sudden cardiac death (SCD). We conducted a review of the literature about ACM and its implications in Sport Cardiology and summarized the main findings in this topic. Early identification of affected athletes through preparticipation screening (PPS) is fundamental but, while classical right-ventricular or biventricular phenotypes are usually suspected because of electrocardiogram (ECG) and echocardiographic abnormalities, variants with predominant left ventricular involvement are often characterized by normal ECG and unremarkable echocardiography. Usually the only manifestations of such variants are exercise-induced VAs and for this reason exercise testing may empower the diagnostic yield of the PPS. Patients with ACM are not eligible to competitive sports activity, but low-to-moderate intensity physical activity under medical supervision is possible in most cases.

Maturation and Function of the Intercalated Disc: Report of Two Pediatric Cases Focusing on Cardiac Development and Myocardial Hyperplasia

The development of the normal human heart, ranging from gestational age to the mature adult heart, relies on a very delicate and timely orchestrated order of processes. One of the most striking alterations in time is the gradual extinction of the ability for cardiomyocytes to proliferate. Once passing this event, cardiomyocytes grow and increase in contractile strength by means of physiological hypertrophy. This process, importantly, seems to depend on an adequate development of electromechanical coupling that is achieved by the appropriate formation of the intercellular junction named the intercalated disc (ICD). In this report, we describe two sudden death cases of young and apparently healthy-born individuals without external abnormalities compared to an age-matched control. Histological examination, including the comparison with the age-matched and histology-matched controls, showed a disturbed formation of the protein machinery composing the electromechanical junctions at the ICD and an increased nuclei count for both patients. As a cause or consequence, cardiomyocytes in both sudden death cases showed signs of a delayed developmental stage, presumably resulting in an exaggerated degree of hyperplasia.

Desmosomal Arrhythmogenic Cardiomyopathy: The Story Telling of a Genetically Determined Heart Muscle Disease

The history of arrhythmogenic cardiomyopathy (AC) as a genetically determined desmosomal disease started since the original discovery by Lancisi in a four-generation family, published in 1728. Contemporary history at the University of Padua started with Dalla Volta, who haemodynamically investigated patients with "auricularization" of the right ventricle, and with Nava, who confirmed familiarity. The contemporary knowledge advances consisted of (a) AC as a heart muscle disease with peculiar electrical instability of the right ventricle; (b) the finding of pathological substrates, in keeping with a myocardial dystrophy; (c) the inclusion of AC in the cardiomyopathies classification; (d) AC as the main cause of sudden death in athletes; (e) the discovery of the culprit genes coding proteins of the intercalated disc (desmosome); (f) progression in clinical diagnosis with specific ECG abnormalities, angiocardiography, endomyocardial biopsy, 2D echocardiography, electron anatomic mapping and cardiac magnetic resonance; (g) the discovery of left ventricular AC; (h) prevention of SCD with the invention and application of the lifesaving implantable cardioverter defibrillator and external defibrillator scattered in public places and playgrounds as well as the ineligibility for competitive sport activity for AC patients; (i) genetic screening of the proband family to unmask asymptomatic carriers. Nondesmosomal ACs, with a phenotype overlapping desmosomal AC, are also treated, including genetics: Transmembrane protein 43, SCN5A, Desmin, Phospholamban, Lamin A/C, Filamin C, Cadherin 2, Tight junction protein 1.

Catalytic antibodies in arrhythmogenic cardiomyopathy patients cleave desmoglein 2 and N-cadherin and impair cardiomyocyte cohesion

AIMS

Arrhythmogenic cardiomyopathy (AC) is a severe heart disease predisposing to ventricular arrhythmias and sudden cardiac death caused by mutations affecting intercalated disc (ICD) proteins and aggravated by physical exercise. Recently, autoantibodies targeting ICD proteins, including the desmosomal cadherin desmoglein 2 (DSG2), were reported in AC patients and were considered relevant for disease development and progression, particularly in patients without underlying pathogenic mutations. However, it is unclear at present whether these autoantibodies are pathogenic and by which mechanisms show specificity for DSG2 and thus can be used as a diagnostic tool.

METHODS AND RESULTS

IgG fractions were purified from 15 AC patients and 4 healthy controls. Immunostainings dissociation assays, atomic force microscopy (AFM), Western blot analysis and Triton X-100 assays were performed utilizing human heart left ventricle tissue, HL-1 cells and murine cardiac slices. Immunostainings revealed that autoantibodies against ICD proteins are prevalent in AC and most autoantibody fractions have catalytic properties and cleave the ICD adhesion molecules DSG2 and N-cadherin, thereby reducing cadherin interactions as revealed by AFM. Furthermore, most of the AC-IgG fractions causing loss of cardiomyocyte cohesion activated p38MAPK, which is known to contribute to a loss of desmosomal adhesion in different cell types, including cardiomyocytes. In addition, p38MAPK inhibition rescued the loss of cardiomyocyte cohesion induced by AC-IgGs.

CONCLUSION

Our study demonstrates that catalytic autoantibodies play a pathogenic role by cleaving ICD cadherins and thereby reducing cardiomyocyte cohesion by a mechanism involving p38MAPK activation. Finally, we conclude that DSG2 cleavage by autoantibodies could be used as a diagnostic tool for AC.

Cheek-Pro-Heart: What Can the Buccal Mucosa Do for Arrhythmogenic Cardiomyopathy?

Arrhythmogenic cardiomyopathy (ACM) is a heart muscle disease associated with ventricular arrhythmias and a high risk of sudden cardiac death (SCD). Although the disease was described over 40 years ago, its diagnosis is still difficult. Several studies have identified a set of five proteins (plakoglobin, Cx43, Nav1.5, SAP97 and GSK3β), which are consistently re-distributed in myocardial samples from ACM patients. Not all protein shifts are specific to ACM, but their combination has provided us with a molecular signature for the disease, which has greatly aided post-mortem diagnosis of SCD victims. The use of this signature, however, was heretofore restricted in living patients, as the analysis requires a heart sample. Recent studies have shown that buccal cells behave similarly to the heart in terms of protein re-localization. Protein shifts are associated with disease onset, deterioration and favorable response to anti-arrhythmic therapy. Accordingly, buccal cells can be used as a surrogate for the myocardium to aid diagnosis, risk stratification and even monitor response to pharmaceutical interventions. Buccal cells can also be kept in culture, hence providing an ex vivo model from the patient, which can offer insights into the mechanisms of disease pathogenesis, including drug response. This review summarizes how the cheek can aid the heart in the battle against ACM.

Desmosomal protein degradation as an underlying cause of arrhythmogenic cardiomyopathy

Arrhythmogenic cardiomyopathy (ACM) is an inherited progressive cardiac disease. Many patients with ACM harbor mutations in desmosomal genes, predominantly in plakophilin-2 (PKP2). Although the genetic basis of ACM is well characterized, the underlying disease-driving mechanisms remain unresolved. Explanted hearts from patients with ACM had less PKP2 compared with healthy hearts, which correlated with reduced expression of desmosomal and adherens junction (AJ) proteins. These proteins were also disorganized in areas of fibrotic remodeling. In vitro data from human-induced pluripotent stem cell-derived cardiomyocytes and microtissues carrying the heterozygous PKP2 c.2013delC pathogenic mutation also displayed impaired contractility. Knockin mice carrying the equivalent heterozygous Pkp2 c.1755delA mutation recapitulated changes in desmosomal and AJ proteins and displayed cardiac dysfunction and fibrosis with age. Global proteomics analysis of 4-month-old heterozygous Pkp2 c.1755delA hearts indicated involvement of the ubiquitin-proteasome system (UPS) in ACM pathogenesis. Inhibition of the UPS in mutant mice increased area composita proteins and improved calcium dynamics in isolated cardiomyocytes. Additional proteomics analyses identified lysine ubiquitination sites on the desmosomal proteins, which were more ubiquitinated in mutant mice. In summary, we show that a plakophilin-2 mutation can lead to decreased desmosomal and AJ protein expression through a UPS-dependent mechanism, which preceded cardiac remodeling. These findings suggest that targeting protein degradation and improving desmosomal protein stability may be a potential therapeutic strategy for the treatment of ACM.

Advances in Ion Channel, Non-Desmosomal Variants and Autophagic Mechanisms Implicated in Arrhythmogenic Cardiomyopathy

Arrhythmogenic cardiomyopathy (ACM) is a heterogeneous disorder characterized by the replacement of cardiac myocytes with fibro-fatty tissues, leading to abnormal excitation-contraction (EC) coupling and a range of malignant events, such as ventricular tachycardia (VT), sudden cardiac death/arrest (SCD/A) and heart failure (HF). The concept of ACM has recently been ex-tended to include right ventricular cardiomyopathy (ARVC), left ventricular cardiomyopathy (ALVC) and biventricular cardiomyopathy. ARVC is generally seen as the most common type of ACM. The pathogenesis of ACM involves mutation variants in desmosomal or non-desmosomal gene loci, as well as various external factors, such as intense exercise, stress and infections. Ion channel alterations, autophagy and non-desmosomal variants are also important components in the development of ACM. As clinical practice enters the era of precision therapy, it is important to review recent studies on these topics to better diagnose and treat the molecular phase of ACM.

Epigenetics in LMNA-Related Cardiomyopathy

Mutations in the gene for lamin A/C (LMNA) cause a diverse range of diseases known as laminopathies. LMNA-related cardiomyopathy is a common inherited heart disease and is highly penetrant with a poor prognosis. In the past years, numerous investigations using mouse models, stem cell technologies, and patient samples have characterized the phenotypic diversity caused by specific LMNA variants and contributed to understanding the molecular mechanisms underlying the pathogenesis of heart disease. As a component of the nuclear envelope, LMNA regulates nuclear mechanostability and function, chromatin organization, and gene transcription. This review will focus on the different cardiomyopathies caused by LMNA mutations, address the role of LMNA in chromatin organization and gene regulation, and discuss how these processes go awry in heart disease.

Diagnosis and management of arrhythmogenic right ventricular cardiomyopathy

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a genetic disorder of the myocardium that can lead to ventricular arrhythmia and sudden cardiac death. The condition has been identified as a significant cause of arrhythmic death among young people and athletes, therefore, early recognition of the disease by emergency clinicians is critical to prevent subsequent death. The diagnosis of ARVC can be very challenging and requires a systematic approach. This publication reviews the pathophysiology, classification, clinical presentations, and appropriate approach to diagnosis and management of ARVC.

Using Zebrafish Animal Model to Study the Genetic Underpinning and Mechanism of Arrhythmogenic Cardiomyopathy

Arrhythmogenic cardiomyopathy (ACM) is largely an autosomal dominant genetic disorder manifesting fibrofatty infiltration and ventricular arrhythmia with predominantly right ventricular involvement. ACM is one of the major conditions associated with an increased risk of sudden cardiac death, most notably in young individuals and athletes. ACM has strong genetic determinants, and genetic variants in more than 25 genes have been identified to be associated with ACM, accounting for approximately 60% of ACM cases. Genetic studies of ACM in vertebrate animal models such as zebrafish (Danio rerio), which are highly amenable to large-scale genetic and drug screenings, offer unique opportunities to identify and functionally assess new genetic variants associated with ACM and to dissect the underlying molecular and cellular mechanisms at the whole-organism level. Here, we summarize key genes implicated in ACM. We discuss the use of zebrafish models, categorized according to gene manipulation approaches, such as gene knockdown, gene knock-out, transgenic overexpression, and CRISPR/Cas9-mediated knock-in, to study the genetic underpinning and mechanism of ACM. Information gained from genetic and pharmacogenomic studies in such animal models can not only increase our understanding of the pathophysiology of disease progression, but also guide disease diagnosis, prognosis, and the development of innovative therapeutic strategies.

Circadian and Seasonal Pattern of Arrhythmic Events in Arrhythmogenic Cardiomyopathy Patients

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited cardiac disease associated with an increased risk of life-threatening arrhythmias. The aim of the present study was to evaluate the association of ventricular arrhythmias (VA) with circadian and seasonal variation in ARVC. One hundred two ARVC patients with an implantable cardioverter defibrillator (ICD) were enrolled in the study. Arrhythmic events included (a) any initial ventricular tachycardia (VT) or fibrillation (VF) prompting ICD implantation, (b) any VT or non-sustained VT (NSVT) recorded by the ICD, and (c) appropriate ICD shocks/therapy. Differences in the annual incidence of events across seasons (winter, spring, summer, autumn) and period of the day (night, morning, afternoon, evening) were assessed both for all cardiac events and major arrhythmic events. In total, 67 events prior to implantation and 263 ICD events were recorded. These included 135 major (58 ICD therapies, 57 self-terminating VT, 20 sustained VT) and 148 minor (NSVT) events. A significant increase in the frequency of events was observed in the afternoon versus in the nights and mornings (p = 0.016). The lowest number of events was registered in the summer, with a peak in the winter (p < 0.001). Results were also confirmed when excluding NSVT. Arrhythmic events in ARVC follow a seasonal variation and a circadian rhythm. They are more prevalent in the late afternoon, the most active period of the day, and in the winter, supporting the role of physical activity and inflammation as triggers of events.

Integrative analysis of Iso-Seq and RNA-seq reveals dynamic changes of alternative promoter, alternative splicing and alternative polyadenylation during Angiotensin II-induced senescence in rat primary aortic endothelial cells

In eukaryotes, alternative promoter (AP), alternative splicing (AS), and alternative polyadenylation (APA) are three crucial regulatory mechanisms that modulate message RNA (mRNA) diversity. Although AP, AS and APA are involved in diverse biological processess, whether they have dynamic changes in Angiotensin II (Ang II) induced senescence in rat primary aortic endothelial cells (RAECs), an important cellular model for studying cardiovascular disease, remains unclear. Here we integrated both PacBio single-molecule long-read isoform sequencing (Iso-Seq) and Illumina short-read RNA sequencing (RNA-seq) to analyze the changes of AP, AS and APA in Ang II-induced senescent RAECs. Iso-Seq generated 36,278 isoforms from 10,145 gene loci and 65.81% of these isoforms are novel, which were further cross-validated by public data obtained by other techonologies such as CAGE, PolyA-Seq and 3'READS. APA contributed most to novel isoforms, followed by AS and AP. Further investigation showed that AP, AS and APA could all contribute to the regulation of isoform, but AS has more dynamic changes compared to AP and APA upon Ang II stimulation. Genes undergoing AP, AS and APA in Ang II-treated cells are enriched in various pathways related to aging or senescence, suggesting that these molecular changes are involved in functional alterations during Ang II-induced senescence. Together, the present study largely improved the annotation of rat genome and revealed gene expression changes at isoform level, extending the understanding of the complexity of gene regulation in Ang II-treated RAECs, and also provided novel clues for discovering the regulatory mechanism undelying Ang II caused vascular senescence and diseases.

Revisiting the Newly Modified Criteria for Arrhythmogenic Right Ventricular Cardiomyopathy/Dysplasia (ARVC/D) and Reporting Newly Identified Genes

Background: Arrhythmogenic Right Ventricular Cardiomyopathy/Dysplasia is an inherited cardiomyopathy, characterized by replacement of the RV muscle wall with fibrofatty tissue. The diagnosis is challenging, due to the absence of a unique presentation and a lack of specific reproducible diagnostic criteria. Materials and methods: Slides and additional clinical information including follow up from 16 cases were reviewed. Pediatric criteria of >30% of muscle replacement was used, instead of >40% as used in adults. Results: All 16 cases were confirmed by genetic testing and show ARVC/D. Applying the adult criteria, 7 cases would not have been categorized as ARVC/D. Conclusion: The modified pediatric criteria for ARVC/D should be used for pediatric patients. Better detection will aid in genetic counseling in order to identify those additional family members susceptible to sudden cardiac deaths so they can be followed optimally.

Modern genomic techniques in the identification of genetic causes of cardiomyopathy

Over the past three decades numerous disease-causing genes have been linked to the pathogenesis of heritable cardiomyopathies, but many causal genes are yet to be identified. Next-generation sequencing (NGS) platforms have revolutionised clinical testing capacity in familial cardiomyopathy. In this review, we summarise how NGS technologies have advanced our understanding of genetic non-syndromic cardiomyopathy over the last decade. First, 26 putative new disease-causing genes have been identified to date, mostly from whole-exome sequencing, and some of which (FLNC, MTO1, HCN4) have had a considerable clinical impact and are now included in routine diagnostic gene panels. Second, we consider challenges in variant interpretation and the importance of large-scale NGS population control cohorts for this purpose. Third, an emerging role of common variation in some forms of genetic cardiomyopathy is being elucidated through recent studies which have illustrated an additive effect of numerous polymorphic loci on cardiac parameters; this may explain phenotypic variability and low rates of genetic diagnosis from sequencing studies. Finally, we discuss the clinical utility of genetic testing in cardiomyopathy in Western settings, where NGS panel testing of core disease genes is currently recommended with possible implications for patient management. Given the findings of recent studies, whole-exome or whole-genome sequencing should be considered in patients of non-European ancestry with clearly familial disease, or severe paediatric disease, when no result is obtained on panel sequencing. The clinical utility of polygenic risk assessment needs to be investigated further in patients with unexplained dilated cardiomyopathy and hypertrophic cardiomyopathy in whom a pathogenic variant is not identified.

Genotype-phenotype Correlates in Arrhythmogenic Cardiomyopathies

PURPOSE OF THE REVIEW

The definition of arrhythmogenic cardiomyopathy (ACM) has expanded beyond desmosomal arrhythmogenic right ventricular cardiomyopathy (ARVC) to include other genetic cardiomyopathies with a significant arrhythmia burden. Emerging data on genotype-phenotype correlations has led recent consensus guidelines to urge genetic testing as a critical component of not only diagnosis but also management of ACM.

RECENT FINDINGS

Plakophilin-2 (PKP2) ARVC/ACM is most likely to meet ARVC Task Force Criteria with right sided involvement and ventricular arrhythmias, while desmoplakin (DSP) ACM may have a normal electrocardiogram (ECG) and has a subepicardial LV scar pattern. Extra-desmosomal ACM including ACM associated with transmembrane protein 43 and phospholamban variants may have characteristic ECG patterns and biventricular cardiomyopathy. Lamin A/C and SCN5A cardiomyopathy often have heart block on ECG with DCM, but are distinct from DCM in that they have significantly elevated arrhythmic risk. Newer genes, especially filamin-C (FLNC) also may have distinct imaging scar patterns, arrhythmia risk, and risk predictors. Recognition of these key differences have implications for clinical management and reinforce the importance of genetic testing in the diagnosis and the emerging opportunities for genotype-specific management of ACM patients.

Acylation-stimulating protein and heart failure progression in arrhythmogenic right ventricular cardiomyopathy

AIMS

Our previous studies suggested that the complement system was critical in the prognosis of arrhythmogenic right ventricular cardiomyopathy (ARVC). The acylation-stimulating protein (ASP), generated through the alternate complement pathway, was reported to regulate lipogenesis and triglyceride storage. This study aimed to investigate the role of ASP in predicting adverse cardiac events in an ARVC cohort.

METHODS AND RESULTS

We enrolled 111 ARVC patients and 106 healthy volunteers, and measured their plasma ASP levels using enzyme-linked immunosorbent assays. Plasma ASP levels were significantly higher in the ARVC patients than in the healthy controls (2325.22 ± 20.08 vs. 2189.75 ± 15.55, P < 0.001), with a similar trend observed in the myocardial explant assay. Spearman correlation analysis indicated plasma ASP level associated with cardiac structural (right ventricular internal dimension, P = 0.006) and functional remodelling (left ventricular ejection fraction, P = 0.002) in ARVC patients. The ARVC patients were followed up for an average of 17.79 ± 1.09 months. Heart failure-associated events (HFAEs) were defined as heart transplantation, on a cardiac transplant list, or death due to end-stage heart failure. Plasma ASP levels in patients with HFAEs were significantly higher than in those without clinical events (2486.03 ± 26.70 vs. 2268.83 ± 23.51, P < 0.001) or those with malignant arrhythmic events (2486.03 ± 26.70 vs. 2297.80 ± 60.46, P = 0.008). LASSO (least absolute shrinkage and selection operator) and multivariable Cox regression analyses showed the ASP level (HR = 1.004, 95% CI [1.002,1.006], P = 0.002) was an independent predictor for adverse HFAEs in ARVC patients. The spline-fitting procedure was applied to illustrate the HFAE-free probabilities at different time points.

CONCLUSIONS

Our results suggest that plasma ASP may be a useful biomarker in prediction of adverse HF-associated events in ARVC patients.

Identification of a novel variant in N-cadherin associated with dilated cardiomyopathy

Background

Dilated cardiomyopathy (DCM), which is a major cause of heart failure, is a primary cardiac muscle disease with high morbidity and mortality rates. DCM is a genetically heritable disease and more than 10 gene ontologies have been implicated in DCM. CDH2 encodes N-cadherin and belongs to a superfamily of transmembrane proteins that mediate cell–cell adhesion in a calcium-dependent manner. Deficiency of CDH2 is associated with arrhythmogenic right ventricular cardiomyopathy (OMIM: 618920) and agenesis of the corpus callosum, cardiac, ocular, and genital syndrome (OMIM: 618929). However, there have been no reports of isolated DCM associated with CDH2 deficiency.

Methods

We performed whole exome sequencing in a 12-year-old girl with non-syndromic DCM and her unaffected parents. Variants in both known DCM-related genes and novel candidate genes were analyzed and pathogenicity confirmation experiments were performed.

Results

No pathogenic/likely pathogenic variant in known DCM-related genes was identified in the patient. We found a de novo variant in a candidate gene CDH2 in the patient, namely, c.474G>C/p.Lys158Asn (NM_001792.5). This variant has not been reported in the ClinVar or Human Gene Mutation Database (HGMD). CDH2 p.Lys158Asn was found in the conserved domain of N-cadherin, which is associated with the hydrolysis of the precursor segment and interference with adhesiveness. Furthermore, we tested the expression and efficiency of cell–cell adhesion while overexpressing the CDH2 Lys158Asn mutant and two previously reported variants in CDH2 as positive controls. The adhesion efficiency was considerably reduced in the presence of the mutated CDH2 protein compared with wild-type CDH2 protein, which suggested that the mutated CDH2 protein's adhesion capacity was impaired. The variant was probably pathogenic after integrating clinical manifestations, genetic analysis, and functional tests.

Conclusion

We identified a CDH2 variant in DCM. We observed a new clinical symptom associated with N-cadherin deficiency and broadened the genetic spectra of DCM.

Rare Variants in Novel Candidate Genes Associated With Nonsyndromic Patent Ductus Arteriosus Identified With Whole-Exome Sequencing

Background: Patent ductus arteriosus (PDA) is one of the most common congenital heart defects causing pulmonary hypertension, infective endocarditis, and even death. The important role of genetics in determining spontaneous ductal closure has been well-established. However, as many of the identified variants are rare, thorough identification of the associated genetic factors is necessary to further explore the genetic etiology of PDA.

Methods: We performed whole-exome sequencing (WES) on 39 isolated nonsyndromic PDA patients and 100 healthy controls. Rare variants and novel genes were identified through bioinformatic filtering strategies. The expression patterns of candidate genes were explored in human embryo heart samples.

Results: Eighteen rare damaging variants of six novel PDA-associated genes (SOX8, NES, CDH2, ANK3, EIF4G1, and HIPK1) were newly identified, which were highly expressed in human embryo hearts.

Conclusions: WES is an efficient diagnostic tool for exploring the genetic pathogenesis of PDA. These findings contribute new insights into the molecular basis of PDA and may inform further studies on genetic risk factors for congenital heart defects.

Atomic Force Microscopy (AFM) Applications in Arrhythmogenic Cardiomyopathy

Arrhythmogenic cardiomyopathy (ACM) is an inherited heart muscle disorder characterized by progressive replacement of cardiomyocytes by fibrofatty tissue, ventricular dilatation, cardiac dysfunction, arrhythmias, and sudden cardiac death. Interest in molecular biomechanics for these disorders is constantly growing. Atomic force microscopy (AFM) is a well-established technic to study the mechanobiology of biological samples under physiological and pathological conditions at the cellular scale. However, a review which described all the different data that can be obtained using the AFM (cell elasticity, adhesion behavior, viscoelasticity, beating force, and frequency) is still missing. In this review, we will discuss several techniques that highlight the potential of AFM to be used as a tool for assessing the biomechanics involved in ACM. Indeed, analysis of genetically mutated cells with AFM reveal abnormalities of the cytoskeleton, cell membrane structures, and defects of contractility. The higher the Young’s modulus, the stiffer the cell, and it is well known that abnormal tissue stiffness is symptomatic of a range of diseases. The cell beating force and frequency provide information during the depolarization and repolarization phases, complementary to cell electrophysiology (calcium imaging, MEA, patch clamp). In addition, original data is also presented to emphasize the unique potential of AFM as a tool to assess fibrosis in cardiac tissue.

Loxl2 is a mediator of cardiac aging in Drosophila melanogaster, genetically examining the role of aging clock genes

Transcriptomic, proteomic, and methylation aging clocks demonstrate that aging has a predictable preset program, while transcriptome trajectory turning points indicate that the 20-40 age range in humans is the likely stage at which the progressive loss of homeostatic control, and in turn aging, begins to have detrimental effects. Turning points in this age range overlapping with human aging clock genes revealed five candidates that we hypothesized could play a role in aging or age-related physiological decline. To examine these gene's effects on lifespan and health-span, we utilized whole body and heart-specific gene knockdown of human orthologs in Drosophila melanogaster. Whole body lysyl oxidase like 2 (Loxl2), fz3, and Glo1 RNAi positively affected lifespan as did heart-specific Loxl2 knockdown. Loxl2 inhibition concurrently reduced age-related cardiac arrythmia and collagen (Pericardin) fiber width. Loxl2 binds several transcription factors in humans and RT-qPCR confirmed that a conserved transcriptional target CDH1 (Drosophila CadN2) has expression levels which correlate with Loxl2 reduction in Drosophila. These results point to conserved pathways and multiple mechanisms by which inhibition of Loxl2 can be beneficial to heart health and organismal aging.

Histopathological Features and Protein Markers of Arrhythmogenic Cardiomyopathy

Arrhythmogenic cardiomyopathy (ACM) is a heritable heart muscle disease characterized by syncope, palpitations, ventricular arrhythmias and sudden cardiac death (SCD) especially in young individuals. It is estimated to affect 1:5,000 individuals in the general population, with >60% of patients bearing one or more mutations in genes coding for desmosomal proteins. Desmosomes are intercellular adhesion junctions, which in cardiac myocytes reside within the intercalated disks (IDs), the areas of mechanical and electrical cell-cell coupling. Histologically, ACM is characterized by fibrofatty replacement of cardiac myocytes predominantly in the right ventricular free wall though left ventricular and biventricular forms have also been described. The disease is characterized by age-related progression, vast phenotypic manifestation and incomplete penetrance, making proband diagnosis and risk stratification of family members particularly challenging. Key protein redistribution at the IDs may represent a specific diagnostic marker but its applicability is still limited by the need for a myocardial sample. Specific markers of ACM in surrogate tissues, such as the blood and the buccal epithelium, may represent a non-invasive, safe and inexpensive alternative for diagnosis and cascade screening. In this review, we shall cover the most relevant biomarkers so far reported and discuss their potential impact on the diagnosis, prognosis and management of ACM.

MicroRNAs: From Junk RNA to Life Regulators and Their Role in Cardiovascular Disease

MicroRNAs (miRNAs) are single-stranded small non-coding RNA (18–25 nucleotides) that until a few years ago were considered junk RNA. In the last twenty years, they have acquired more importance thanks to the understanding of their influence on gene expression and their role as negative regulators at post-transcriptional level, influencing the stability of messenger RNA (mRNA). Approximately 5% of the genome encodes miRNAs which are responsible for regulating numerous signaling pathways, cellular processes and cell-to-cell communication. In the cardiovascular system, miRNAs control the functions of various cells, such as cardiomyocytes, endothelial cells, smooth muscle cells and fibroblasts, playing a role in physiological and pathological processes and seeming also related to variations in contractility and hereditary cardiomyopathies. They provide a new perspective on the pathophysiology of disorders such as hypertrophy, fibrosis, arrhythmia, inflammation and atherosclerosis. MiRNAs are differentially expressed in diseased tissue and can be released into the circulation and then detected. MiRNAs have become interesting for the development of new diagnostic and therapeutic tools for various diseases, including heart disease. In this review, the concept of miRNAs and their role in cardiomyopathies will be introduced, focusing on their potential as therapeutic and diagnostic targets (as biomarkers).

Plakophilin-2 truncating variants impair cardiac contractility by disrupting sarcomere stability and organization

Progressive loss of cardiac systolic function in arrhythmogenic cardiomyopathy (ACM) has recently gained attention as an important clinical consideration in managing the disease. However, the mechanisms leading to reduction in cardiac contractility are poorly defined. Here, we use CRISPR gene editing to generate human induced pluripotent stem cells (iPSCs) that harbor plakophilin-2 truncating variants (PKP2tv), the most prevalent ACM-linked mutations. The PKP2tv iPSC–derived cardiomyocytes are shown to have aberrant action potentials and reduced systolic function in cardiac microtissues, recapitulating both the electrical and mechanical pathologies reported in ACM. By combining cell micropatterning with traction force microscopy and live imaging, we found that PKP2tvs impair cardiac tissue contractility by destabilizing cell-cell junctions and in turn disrupting sarcomere stability and organization. These findings highlight the interplay between cell-cell adhesions and sarcomeres required for stabilizing cardiomyocyte structure and function and suggest fundamental pathogenic mechanisms that may be shared among different types of cardiomyopathies.

Haploinsufficiency of Tmem43 in cardiac myocytes activates the DNA damage response pathway leading to a late-onset senescence-associated pro-fibrotic cardiomyopathy

AIMS

Arrhythmogenic cardiomyopathy (ACM) encompasses a genetically heterogeneous group of myocardial diseases whose manifestations are sudden cardiac death, cardiac arrhythmias, heart failure, and in a subset fibro-adipogenic infiltration of the myocardium. Mutations in the TMEM43 gene, encoding transmembrane protein 43 (TMEM43) are known to cause ACM. The purpose of the study was to gain insights into the molecular pathogenesis of ACM caused by TMEM43 haploinsufficiency.

METHODS AND RESULTS

The Tmem43 gene was specifically deleted in cardiac myocytes by crossing the Myh6-Cre and floxed Tmem43 mice. Myh6-Cre:Tmem43W/F mice showed an age-dependent phenotype characterized by an increased mortality, cardiac dilatation and dysfunction, myocardial fibrosis, adipogenesis, and apoptosis. Sequencing of cardiac myocyte transcripts prior to and after the onset of cardiac phenotype predicted early activation of the TP53 pathway. Increased TP53 activity was associated with increased levels of markers of DNA damage response (DDR), and a subset of senescence-associated secretary phenotype (SASP). Activation of DDR, TP53, SASP, and their selected downstream effectors, including phospho-SMAD2 and phospho-SMAD3 were validated by alternative methods, including immunoblotting. Expression of SASP was associated with epithelial-mesenchymal transition and age-dependent expression of myocardial fibrosis and apoptosis in the Myh6-Cre:Tmem43W/F mice.

CONCLUSION

TMEM43 haploinsufficiency is associated with activation of the DDR and the TP53 pathways, which lead to increased expression of SASP and an age-dependent expression of a pro-fibrotic cardiomyopathy. Given that TMEM43 is a nuclear envelope protein and our previous data showing deficiency of another nuclear envelope protein, namely lamin A/C, activates the DDR/TP53 pathway, we surmise that DNA damage is a shared mechanism in the pathogenesis of cardiomyopathies caused by mutations involving nuclear envelope proteins.

Pharmacological suppression of the WNT signaling pathway attenuates age-dependent expression of the phenotype in a mouse model of arrhythmogenic cardiomyopathy

Introduction

Arrhythmogenic cardiomyopathy (ACM) is a genetic disease of the myocardium, characterized by cardiac arrhythmias, dysfunction, and sudden cardiac death. The pathological hallmark of ACM is fibro-adipocytes replacing cardiac myocytes. The canonical WNT pathway is implicated in the pathogenesis of ACM.

Aim

The study aimed to determine the effects of the suppression of the WNT pathway on cardiac phenotype in a mouse model of ACM.

Methods and Results

One copy of the Dsp gene, a known cause of ACM in humans, was deleted specifically in cardiac myocytes (Myh6-Cre-Dsp ^W/F). Three-month-old wild type and Myh6-Cre-Dsp ^W/F mice, without a discernible phenotype, were randomized to either untreated or daily administration of a vehicle (placebo), or WNT974, the latter an established inhibitor of the WNT pathway, for three months. The Myh6-Cre-Dsp ^W/F mice in the untreated or placebo-treated groups exhibited cardiac dilatation and dysfunction, increased myocardial fibrosis, and apoptosis upon completion of the study, which was verified by complementary methods. Daily administration of WNT974 prevented and/or attenuated evolving cardiac dilatation and dysfunction, normalized myocardial fibrosis, and reduced apoptosis, compared to the untreated or placebo-treated groups. However, administration of WNT974 increased the number of adipocytes only in the Myh6-Cre-Dsp ^W/F hearts. There were no differences in the incidence of cardiac arrhythmias and survival rates.

Conclusion

Suppression of the WNT pathway imparts salutary phenotypic effects by preventing or attenuating age-dependent expression of cardiac dilatation and dysfunction, myocardial fibrosis, and apoptosis in a mouse model of ACM. The findings set the stage for large-scale studies and studies in larger animal models to test the beneficial effects of the suppression of the WNT pathway in ACM.

One sentence summary

Suppression of the WNT signaling pathway has beneficial effects on cardiac dysfunction, myocardial apoptosis, and fibrosis in a mouse model of arrhythmogenic cardiomyopathy.

Identification of Hub Genes Associated with the Pathogenesis of Intracranial Aneurysm via Integrated Bioinformatics Analysis

BACKGROUND

At present, the pathogenesis of intracranial aneurysms (IA) remains unclear, which significantly hinders the development of novel strategies for the clinical treatment. In this study, bioinformatics methods were used to identify the potential hub genes and pathways associated with the pathogenesis of IA.

METHODS

The gene expression datasets of patients with intracranial aneurysm were downloaded from the Gene Expression Database (GEO), and the different data sets were integrated by the robust rank aggregation (RRA) method to identify the differentially expressed genes between patients with intracranial aneurysm and the controls. The functional enrichment analyses of the significant differentially expressed genes (DEGs) were performed and the protein-protein interaction (PPI) network was constructed; thereafter, the hub genes were screened by cytoHubba plug-in of Cytoscape, and finally sequencing dataset GSE122897 was used to verify the hub genes.

RESULTS

The GSE15629, GSE75436, GSE26969, and GSE6551 expression profiles have been included in this study, including 34 intracranial aneurysm samples and 26 control samples. The four datasets obtained 136 significant DEGs (45 up-regulated, 91 down-regulated). Enrichment analysis showed that the extracellular matrix structural constituent and the ECM-receptor interaction were closely related to the occurrence of IA. It was finally determined that eight hub genes associated with the development of IA, including VCAN, COL1A1, COL11A1, COL5A1, COL5A2, POSTN, THBS2, and CDH2.

CONCLUSION

The discovery of potential hub genes and pathways could enhance the understanding of the molecular mechanisms associated with the development of IA. These hub genes may be potential therapeutic targets for the management and new biomarker for the diagnosis of IA.

Arrhythmogenic Cardiomyopathy-Current Treatment and Future Options

Arrhythmogenic cardiomyopathy (ACM) is an inheritable heart muscle disease characterised pathologically by fibrofatty myocardial replacement and clinically by ventricular arrhythmias (VAs) and sudden cardiac death (SCD). Although, in its original description, the disease was believed to predominantly involve the right ventricle, biventricular and left-dominant variants, in which the myocardial lesions affect in parallel or even mostly the left ventricle, are nowadays commonly observed. The clinical management of these patients has two main purposes: the prevention of SCD and the control of arrhythmic and heart failure (HF) events. An implantable cardioverter defibrillator (ICD) is the only proven lifesaving treatment, despite significant morbidity because of device-related complications and inappropriate shocks. Selection of patients who can benefit the most from ICD therapy is one of the most challenging issues in clinical practice. Risk stratification in ACM patients is mostly based on arrhythmic burden and ventricular dysfunction severity, although other clinical features resulting from electrocardiogram and imaging modalities such as cardiac magnetic resonance may have a role. Medical therapy is crucial for treatment of VAs and the prevention of negative ventricular remodelling. In this regard, the efficacy of novel anti-HF molecules and drugs acting on the inflammatory pathway in patients with ACM is, to date, unknown. Catheter ablation represents an effective strategy to treat ventricular tachycardia relapses and recurrent ICD shocks. The present review will address the current strategies for prevention of SCD and treatment of VAs and HF in patients with ACM.

Rationale and design of the African Cardiomyopathy and Myocarditis Registry Program: The IMHOTEP study

BACKGROUND

Heart failure (HF), the dominant form of cardiovascular disease in Africans, is mainly due to hypertension, rheumatic heart disease and cardiomyopathy. Cardiomyopathies pose a great challenge because of poor prognosis and high prevalence in low- and middle-income countries (LMICs). Little is known about the etiology and outcome of cardiomyopathy in Africa. Specifically, the role of myocarditis and the genetic causes of cardiomyopathy are largely unidentified in Africans.

METHOD

The African Cardiomyopathy and Myocarditis Registry Program (the IMHOTEP study) is a pan-African multi-centre, hospital-based cohort study, designed with the primary aim of describing the clinical characteristics, genetic causes, prevalence, management and outcome of cardiomyopathy and myocarditis in children and adults. The secondary aim is to identify barriers to the implementation of evidence-based care and provide a platform for trials and other intervention studies to reduce morbidity and mortality in cardiomyopathy. The registry consists of a prospective cohort of newly diagnosed (i.e., incident) cases and a retrospective (i.e., prevalent) cohort of existing cases from participating centres. Patients with cardiomyopathy and myocarditis will be subjected to a standardized 3-stage diagnostic process. To date, 750 patients have been recruited into the multi-centre pilot phase of the study.

CONCLUSION

The IMHOTEP study will provide comprehensive and novel data on clinical features, genetic causes, prevalence and outcome of African children and adults with all forms of cardiomyopathy and myocarditis in Africa. Based on these findings, appropriate strategies for management and prevention of the cardiomyopathies in LMICs are likely to emerge.

Variants in MHY7 Gene Cause Arrhythmogenic Cardiomyopathy

BACKGROUND

Arrhythmogenic Cardiomyopathy (ACM) is a disease of the cardiac muscle, characterized by frequent ventricular arrhythmias and functional/ structural abnormalities, mainly of the right ventricle. To date, 20 different genes have been associated with ACM and the majority of them encode for desmosomal proteins. In this study, we describe the characterization of two novel variants in MHY7 gene, segregating in two ACM families. MYH7 encodes for myosin heavy chain β (MHC-β) isoform, involved in cardiac muscle contractility.

METHOD AND RESULTS

In family A, the autopsy revealed ACM with biventricular involvement in both the proband and his father. In family B, the proband had been diagnosed as affected by ACM and implanted with implantable cardioverter defibrillator (ICD), due to ECG evidence of monomorphic ventricular tachycardia after syncope. After clinical evaluation, a molecular diagnosis was performed using a NGS custom panel. The two novel variants identified predicted damaging, located in a highly conserved domain: c. 2630T>C is not described while c.2609G>A has a frequency of 0.00000398. In silico analyses evaluated the docking characteristics between proteins using the Haddock2.2 webserver.

CONCLUSIONS

Our results reveal two variants in sarcomeric genes to be the molecular cause of ACM, further increasing the genetic heterogeneity of the disease; in fact, sarcomeric variants are usually associated with HCM phenotype. Studies on the role of sarcomere genes in the pathogenesis of ACM are surely recommended in those ACM patients negative for desmosomal mutation screening.

Brugada syndrome and arrhythmogenic cardiomyopathy: overlapping disorders of the connexome?

Arrhythmogenic cardiomyopathy (ACM) and Brugada syndrome (BrS) are inherited diseases characterized by an increased risk for arrhythmias and sudden cardiac death. Possible overlap between the two was suggested soon after the description of BrS. Since then, various studies focusing on different aspects have been published pointing to similar findings in the two diseases. More recent findings on the structure of the cardiac cell-cell junctions may unite the pathophysiology of both diseases and give further evidence to the theory that they may in part be variants of the same disease spectrum. In this review, we aim to summarize the studies indicating the pathophysiological, genetic, structural, and electrophysiological overlap between ACM and BrS.

Arrhythmogenic Left Ventricular Cardiomyopathy: Genotype-Phenotype Correlations and New Diagnostic Criteria

Arrhythmogenic cardiomyopathy (ACM) is an inherited heart muscle disease characterized by loss of ventricular myocardium and fibrofatty replacement, which predisposes to scar-related ventricular arrhythmias and sudden cardiac death, particularly in the young and athletes. Although in its original description the disease was characterized by an exclusive or at least predominant right ventricle (RV) involvement, it has been demonstrated that the fibrofatty scar can also localize in the left ventricle (LV), with the LV lesion that can equalize or even overcome that of the RV. While the right-dominant form is typically associated with mutations in genes encoding for desmosomal proteins, other (non-desmosomal) mutations have been showed to cause the biventricular and left-dominant variants. This has led to a critical evaluation of the 2010 International Task Force criteria, which exclusively addressed the right phenotypic manifestations of ACM. An International Expert consensus document has been recently developed to provide upgraded criteria (“the Padua Criteria”) for the diagnosis of the whole spectrum of ACM phenotypes, particularly left-dominant forms, highlighting the use of cardiac magnetic resonance. This review aims to offer an overview of the current knowledge on the genetic basis, the phenotypic expressions, and the diagnosis of left-sided variants, both biventricular and left-dominant, of ACM.

Identification of Hub Genes and MicroRNAs Associated With Idiopathic Pulmonary Arterial Hypertension by Integrated Bioinformatics Analyses

Objective

The aim of this study is the identification of hub genes associated with idiopathic pulmonary arterial hypertension (IPAH).

Materials and Methods

GSE15197 gene expression data was downloaded from the Gene Expression Omnibus (GEO) database. Differentially expressed genes (DEGs) were identified by screening IPAH patients and controls. The 5,000 genes with the greatest variances were analyzed using a weighted gene co-expression network analysis (WGCNA). Modules with the strongest correlation with IPAH were chosen, followed by a functional enrichment analysis. Protein–protein interaction (PPI) networks were constructed to identify hub gene candidates using calculated degrees. Real hub genes were found from the overlap of DEGs and candidate hub genes. microRNAs (miRNAs) targeting real hub genes were found by screening miRNet 2.0. The most important IPAH miRNAs were identified.

Results

There were 4,395 DEGs identified. WGCNA indicated that green and brown modules associated most strongly with IPAH. Functional enrichment analysis showed that green and brown module genes were mainly involved in protein digestion and absorption and proteoglycans in cancer, respectively. The top ten candidate hub genes in green and brown modules were identified, respectively. After overlapping with DEGs, 11 real hub genes were identified: EP300, MMP2, CDH2, CDK2, GNG10, ALB, SMC2, DHX15, CUL3, BTBD1, and LTN1. These genes were expressed with significant differences in IPAH versus controls, indicating a high diagnostic ability. The miRNA–gene network showed that hsa-mir-1-3p could associate with IPAH.

Conclusion

EP300, MMP2, CDH2, CDK2, GNG10, ALB, SMC2, DHX15, CUL3, BTBD1, and LTN1 may play essential roles in IPAH. Predicted miRNA hsa-mir-1-3p could regulate gene expression in IPAH. Such hub genes may contribute to the pathology and progression in IPAH, providing potential diagnostic and therapeutic opportunities for IPAH patients.

Currarino syndrome: a comprehensive genetic review of a rare congenital disorder

Background

The triad of a presacral mass, sacral agenesis and an anorectal anomaly constitutes the rare Currarino syndrome (CS), which is caused by dorsal–ventral patterning defects during embryonic development. The major causative CS gene is MNX1, encoding a homeobox protein.

Main body

In the majority of patients, CS occurs as an autosomal dominant trait; however, a female predominance observed, implies that CS may underlie an additional mode(s) of inheritance. Often, the diagnosis of CS is established solely by clinical findings, impacting a detailed analysis of the disease. Our combined data, evaluating more than 60 studies reporting patients with CS-associated mutations, revealed a slightly higher incidence rate in females with a female-to-male ratio of 1.39:1. Overall, MNX1 mutation analysis was successful in only 57.4% of all CS patients investigated, with no mutation detected in 7.7% of the familial and 68% of the sporadic patients. Our studies failed to detect the presence of an expressed MNX1 isoform that might explain at least some of these mutation-negative cases.

Conclusion

Aside from MNX1, other genes or regulatory regions may contribute to CS and we discuss several cytogenetic studies and whole-exome sequencing data that have implicated further loci/genes in its etiology.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-01799-0.

International Evidence Based Reappraisal of Genes Associated With Arrhythmogenic Right Ventricular Cardiomyopathy Using the Clinical Genome Resource Framework

BACKGROUND

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited disease characterized by ventricular arrhythmias and progressive ventricular dysfunction. Genetic testing is recommended, and a pathogenic variant in an ARVC-associated gene is a major criterion for diagnosis according to the 2010 Task Force Criteria. As incorrect attribution of a gene to ARVC can contribute to misdiagnosis, we assembled an international multidisciplinary ARVC Clinical Genome Resource Gene Curation Expert Panel to reappraise all reported ARVC genes.

METHODS

Following a comprehensive literature search, six 2-member teams conducted blinded independent curation of reported ARVC genes using the semiquantitative Clinical Genome Resource framework.

RESULTS

Of 26 reported ARVC genes, only 6 (PKP2, DSP, DSG2, DSC2, JUP, and TMEM43) had strong evidence and were classified as definitive for ARVC causation. There was moderate evidence for 2 genes, DES and PLN. The remaining 18 genes had limited or no evidence. RYR2 was refuted as an ARVC gene since clinical data and model systems exhibited a catecholaminergic polymorphic ventricular tachycardia phenotype. In ClinVar, only 5 pathogenic/likely pathogenic variants (1.1%) in limited evidence genes had been reported in ARVC cases in contrast to 450 desmosome gene variants (97.4%).

CONCLUSIONS

Using the Clinical Genome Resource approach to gene-disease curation, only 8 genes (PKP2, DSP, DSG2, DSC2, JUP, TMEM43, PLN, and DES) had definitive or moderate evidence for ARVC, and these genes accounted for nearly all pathogenic/likely pathogenic ARVC variants in ClinVar. Therefore, only pathogenic/likely pathogenic variants in these 8 genes should yield a major criterion for ARVC diagnosis. Pathogenic/likely pathogenic variants identified in other genes in a patient should prompt further phenotyping as variants in many of these genes are associated with other cardiovascular conditions.

Metabolic Signature of Arrhythmogenic Cardiomyopathy

Arrhythmogenic cardiomyopathy (ACM) is a genetic-based cardiac disease accompanied by severe ventricular arrhythmias and a progressive substitution of the myocardium with fibro-fatty tissue. ACM is often associated with sudden cardiac death. Due to the reduced penetrance and variable expressivity, the presence of a genetic defect is not conclusive, thus complicating the diagnosis of ACM. Recent studies on human induced pluripotent stem cells-derived cardiomyocytes (hiPSC-CMs) obtained from ACM individuals showed a dysregulated metabolic status, leading to the hypothesis that ACM pathology is characterized by an impairment in the energy metabolism. However, despite efforts having been made for the identification of ACM specific biomarkers, there is still a substantial lack of information regarding the whole metabolomic profile of ACM patients. The aim of the present study was to investigate the metabolic profiles of ACM patients compared to healthy controls (CTRLs). The targeted Biocrates AbsoluteIDQ^® p180 assay was used on plasma samples. Our analysis showed that ACM patients have a different metabolome compared to CTRLs, and that the pathways mainly affected include tryptophan metabolism, arginine and proline metabolism and beta oxidation of fatty acids. Altogether, our data indicated that the plasma metabolomes of arrhythmogenic cardiomyopathy patients show signs of endothelium damage and impaired nitric oxide (NO), fat, and energy metabolism.

Cadherin 2-Related Arrhythmogenic Cardiomyopathy: Prevalence and Clinical Features

BACKGROUND

Arrhythmogenic cardiomyopathy (ACM) is an inherited cardiac disease characterized by fibrofatty replacement of the right and left ventricle, often causing ventricular dysfunction and life-threatening arrhythmias. Variants in desmosomal genes account for up to 60% of cases. Our objective was to establish the prevalence and clinical features of ACM stemming from pathogenic variants in the nondesmosomal cadherin 2 (CDH2), a novel genetic substrate of ACM.

METHODS

A cohort of 500 unrelated patients with a definite diagnosis of ACM and no disease-causing variants in the main ACM genes was assembled. Genetic screening of CDH2 was performed through next-generation or Sanger sequencing. Whenever possible, cascade screening was initiated in the families of CDH2-positive probands, and clinical evaluation was performed.

RESULTS

Genetic screening of CDH2 led to the identification of 7 rare variants: 5, identified in 6 probands, were classified as pathogenic or likely pathogenic. The previously established p.D407N pathogenic variant was detected in 2 additional probands. Probands and family members with pathogenic/likely pathogenic variants in CDH2 were clinically evaluated, and along with previously published cases, altogether contributed to the identification of gene-specific features (13 cases from this cohort and 11 previously published, for a total of 9 probands and 15 family members). Ventricular arrhythmic events occurred in most CDH2-positive subjects (20/24, 83%), while the occurrence of heart failure was rare (2/24, 8.3%). Among probands, sustained ventricular tachycardia and sudden cardiac death occurred in 5/9 (56%).

CONCLUSIONS

In this worldwide cohort of previously genotype-negative ACM patients, the prevalence of probands with CDH2 pathogenic/likely pathogenic variants was 1.2% (6/500). Our data show that this cohort of CDH2-ACM patients has a high incidence of ventricular arrhythmias, while evolution toward heart failure is rare.

2019 HRS expert consensus statement on evaluation, risk stratification, and management of arrhythmogenic cardiomyopathy: Executive summary

Arrhythmogenic cardiomyopathy (ACM) is an arrhythmogenic disorder of the myocardium not secondary to ischemic, hypertensive, or valvular heart disease. ACM incorporates a broad spectrum of genetic, systemic, infectious, and inflammatory disorders. This designation includes, but is not limited to, arrhythmogenic right/left ventricular cardiomyopathy, cardiac amyloidosis, sarcoidosis, Chagas disease, and left ventricular noncompaction. The ACM phenotype overlaps with other cardiomyopathies, particularly dilated cardiomyopathy with arrhythmia presentation that may be associated with ventricular dilatation and/or impaired systolic function. This expert consensus statement provides the clinician with guidance on evaluation and management of ACM and includes clinically relevant information on genetics and disease mechanisms. PICO questions were utilized to evaluate contemporary evidence and provide clinical guidance related to exercise in arrhythmogenic right ventricular cardiomyopathy. Recommendations were developed and approved by an expert writing group, after a systematic literature search with evidence tables, and discussion of their own clinical experience, to present the current knowledge in the field. Each recommendation is presented using the Class of Recommendation and Level of Evidence system formulated by the American College of Cardiology and the American Heart Association and is accompanied by references and explanatory text to provide essential context. The ongoing recognition of the genetic basis of ACM provides the opportunity to examine the diverse triggers and potential common pathway for the development of disease and arrhythmia.

Mechanotransduction and Adrenergic Stimulation in Arrhythmogenic Cardiomyopathy: An Overview of in vitro and in vivo Models

Arrhythmogenic Cardiomyopathy (AC) is a rare inherited heart disease, manifesting with progressive myocardium degeneration and dysfunction, and life-threatening arrhythmic events that lead to sudden cardiac death. Despite genetic determinants, most of AC patients admitted to hospital are athletes or very physically active people, implying the existence of other disease-causing factors. It is recognized that AC phenotypes are enhanced and triggered by strenuous physical activity, while excessive mechanical stretch and load, and repetitive adrenergic stimulation are mechanisms influencing disease penetrance. Different approaches have been undertaken to recapitulate and study both mechanotransduction and adrenergic signaling in AC, including the use of in vitro cellular and tissue models, and the development of in vivo models (particularly rodents but more recently also zebrafish). However, it remains challenging to reproduce mechanical load stimuli and physical activity in laboratory experimental settings. Thus, more work to drive the innovation of advanced AC models is needed to recapitulate these subtle physiological influences. Here, we review the state-of-the-art in this field both in clinical and laboratory-based modeling scenarios. Specific attention will be focused on highlighting gaps in the knowledge and how they may be resolved by utilizing novel research methodology.

Selection signatures of Fuzhong Buffalo based on whole-genome sequences

BACKGROUND

Fuzhong buffalo, a native breed of Guangxi Zhuang Autonomous Region, is traditionally used as a draft animal to provide farm power in the rice cultivation. In addition, the Fuzhong buffalo also prepared for the bullfighting festival organized by the locals. The detection of the selective signatures in its genome can help in elucidating the selection mechanisms in its stamina and muscle development of a draft animal.

RESULTS

In this study, we analyzed 27 whole genomes of buffalo (including 15 Fuzhong buffalo genomes and 12 published buffalo genomes from Upper Yangtze region). The ZHp, ZFst, π-Ratio, and XP-EHH statistics were used to identify the candidate signatures of positive selection in Fuzhong buffalo. Our results detected a set of candidate genes involving in the pathways and GO terms associated with the response to exercise (e.g., ALDOA, STAT3, AKT2, EIF4E2, CACNA2D2, TCF4, CDH2), immunity (e.g., PTPN22, NKX2-3, PIK3R1, ITK, TMEM173), nervous system (e.g., PTPN21, ROBO1, HOMER1, MAGI2, SLC1A3, NRG3, SNAP47, CTNNA2, ADGRL3). In addition, we also identified several genes related to production and growth traits (e.g., PHLPP1, PRKN, MACF1, UCN3, RALGAPA1, PHKB, PKD1L). Our results depicted several pathways, GO terms, and candidate genes to be associated with response to exercise, immunity, nervous system, and growth traits.

CONCLUSIONS

The selective sweep analysis of the Fuzhong buffalo demonstrated positive selection pressure on potential target genes involved in behavior, immunity, and growth traits, etc. Our findings provided a valuable resource for future research on buffalo breeding and an insight into the mechanisms of artificial selection.

State of the Art Review on Genetics and Precision Medicine in Arrhythmogenic Cardiomyopathy

Arrhythmogenic cardiomyopathy (ACM) is an inherited cardiomyopathy characterised by ventricular arrhythmia and an increased risk of sudden cardiac death (SCD). Numerous genetic determinants and phenotypic manifestations have been discovered in ACM, posing a significant clinical challenge. Further to this, wider evaluation of family members has revealed incomplete penetrance and variable expressivity in ACM, suggesting a complex genotype-phenotype relationship. This review details the genetic basis of ACM with specific genotype-phenotype associations, providing the reader with a nuanced perspective of this condition; whilst also proposing a future roadmap to delivering precision medicine-based management in ACM.

The Role of MicroRNAs in Arrhythmogenic Cardiomyopathy: Biomarkers or Innocent Bystanders of Disease Progression?

Arrhythmogenic cardiomyopathy (AC) is an inherited cardiac disease characterized by a progressive fibro-fatty replacement of the working myocardium and by life-threatening arrhythmias and risk of sudden cardiac death. Pathogenic variants are identified in nearly 50% of affected patients mostly in genes encoding for desmosomal proteins. AC incomplete penetrance and phenotypic variability advocate that other factors than genetics may modulate the disease, such as microRNAs (miRNAs). MiRNAs are small noncoding RNAs with a primary role in gene expression regulation and network of cellular processes. The implication of miRNAs in AC pathogenesis and their role as biomarkers for early disease detection or differential diagnosis has been the objective of multiple studies employing diverse designs and methodologies to detect miRNAs and measure their expression levels. Here we summarize experiments, evidence, and flaws of the different studies and hitherto knowledge of the implication of miRNAs in AC pathogenesis and diagnosis.

Knockout of SORBS2 Protein Disrupts the Structural Integrity of Intercalated Disc and Manifests Features of Arrhythmogenic Cardiomyopathy

Background Sorbs2b (sorbin and SH3 domain-containing 2b) was recently identified as a cardiomyopathy gene from a zebrafish mutagenesis screen. However, cardiac functions of its mammalian ortholog remain elusive. Methods and Results We conducted a detailed expression and subcellular localization analysis of Sorbs2 ortholog in mice and a phenotypic characterization in Sorbs2 knockout mice. Sorbs2 is highly expressed in the mouse heart and encodes an adhesion junction/desmosome protein that is mainly localized to the intercalated disc. A mutation with near complete depletion of the Sorbs2 protein in mice results in phenotypes characteristic of human arrhythmogenic cardiomyopathy (ACM), including right ventricular dilation, right ventricular dysfunction, spontaneous ventricular tachycardia, and premature death. Sorbs2 is required to maintain the structural integrity of intercalated disc. Its absence resulted in profound cardiac electrical remodeling with impaired impulse conduction and action potential derangements. Targeted sequencing of human patients with ACM identified 2 rare splicing variants classified as likely pathogenic were in 2 unrelated individuals with ACM from a cohort of 59 patients with ACM. Conclusions The Sorbs2 knockout mouse manifests several key features reminiscent of human ACM. Although the candidacy of SORBS2 as a new ACM-susceptibility gene is supported by preliminary human genetics study, future validation in larger cohorts with ACM is needed.